1. Field of the Invention
The present invention relates to a read head with an N-cycle switch for electrostatic discharge (ESD) protection and, more particularly, to such a read head which has multiple one cycle switches which can be operated by a laser beam for sequentially shorting and unshorting the read head across a sense current circuit.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider which supports a write head and a read head magnetic head assembly, a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The read head includes a sensor which is located between ferromagnetic first and second shield layers. First and second leads are connected to the sensor and to the processing circuitry for conducting a sense current through the sensor. When the sensor detects signal fields from a track of a rotating magnetic disk the resistance of the sensor changes which changes the potential in the sense current circuit. These potential changes are processed as playback signals by the processing circuitry. Two types of magnetoresistive (MR) sensors are located between nonmagnetic insulative first and second read gap layers which are, in turn, located between the first and second shield layers. One type of magnetoresistive sensor is an anisotropic magnetoresistive (AMR) sensor and the other type is a spin valve (SV) sensor. A third type of sensor is a tunnel valve sensor which may employ the first and second shield layers as first and second lead layers. In this type of sensor the first and second read gap layers may be omitted.
Magnetic head assemblies are constructed on a wafer which has rows and columns of magnetic head assemblies. Multiple thin film layers are typically deposited to form the read head portions followed by multiple thin film layers which are deposited to form the write head portions. The construction at the wafer level embeds each magnetic head assembly in a respective slider portion of the wafer. The wafer is then diced into rows of sliders and lapped to form the aforementioned ABS. Each row of sliders is then diced into individual sliders. One or more sliders are then mounted in the aforementioned disk drive.
The sensor is a very thin component of the read head which may be on the order of 150 xc3x85. A very small current from an unwanted source can destroy the sensor which, in turn, renders the read head inoperable. This unwanted current can reach the sensor through the aforementioned sense current circuitry. During the making of the magnetic head assemblies at the row, slider and individual level the sensor can be subjected to electrostatic discharges (ESDs) which can occur from human handling, plastic objects or other electrical sources. One way of protecting the sensor from ESDs is to short-circuit the sense current circuit. However, when the sensor is to be tested for operability, particularly at the row and individual level, the sense current circuit must be unshorted or open. Accordingly, the sensor needs to be unshorted during periods of testing and shorted during all other times in order to protect the sensor from ESDs. Since multiple tests are required the sensor has to be sequentially unshorted and shorted up to the time it becomes operable in a magnetic disk drive. One technique of unshorting the sensor is found in commonly owned U.S. Pat. No. 5,759,428 wherein a laser is employed for cutting a delete pad, thereby unshorting the sense current circuit.
The present invention provides an apparatus and method for shorting and unshorting a sense current circuit of a sensor in a read head multiple times so that the sensor is alternately protected from ESDs and readied for testing. This is accomplished by providing an N-cycle switch in the sense current circuit, hereinafter referred to as the read head circuit, which has at least one one-cycle switch. In the preferred embodiment the N-cycle switch has multiple one-cycle switches wherein each one-cycle switch includes a shorting switch and an unshorting switch for shorting the read head circuit and unshorting the read head circuit, respectively. Each shorting and unshorting switch is constructed for activation by a laser beam. In one embodiment the shorting switch includes first and second contacts which are separated by an electrically insulative layer which is preferably aluminum oxide (Al2O3). When this switch is subjected to a laser beam of sufficient fluence the first of the first and second contacts melts which, in turn, melts the insulation layer which, in turn, melts the other contact causing the first and second contacts to electrically connect. In another embodiment the shorting switch may be constructed of first and second contacts which are separated by a void. Upon subjecting this switch to a laser beam of sufficient fluence the contact first receiving the laser beam melts into the void contacting and making electrical connection with the other contact.
In the preferred embodiment both of the shorting and unshorting switches are embedded below a surface of the slider so as to protect the contacts from ESDs and contamination. The layer of material of the slider between its surface and the switch is preferably aluminum oxide (Al2O3) with a sufficient thickness to permit penetration of the laser beam to activate either the shorting or the unshorting switch. In a still further preferred embodiment the switches are located in the slider at a predetermined location with respect to the read head and the ABS so that the read head and the ABS may be employed for guiding the laser beam to the appropriate location on the slider for activating either the shorting or the unshorting switch.
An object of the present invention is to provide an N-cycle switch for a read head circuit which can be employed for sequentially shorting and unshorting the read head for sequentially protecting the read head from ESDs and readying it for testing.
Another object is to provide the aforementioned N-cycle switch wherein the shorting and unshorting switches can be activated by a laser beam.
A further object is to provide a method of making the aforementioned N-cycle switch.
Still another object is to provide a method of using the aforementioned N-cycle switch.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.